In recent years, there has been a growing interest in nanosized microstructures applicable for use in functional materials and functional devices.
As a method of fabricating such a microstructure, a method may be mentioned in which a microstructure is directly fabricated by a semiconductor processing technique typified by a fine pattern forming technique, such as photolithography.
Apart from the above-described semiconductor processing technique, there is a technique using the phenomenon of self-organization or self-formation of a material. That is, a novel microstructure is thereby realized on an orderly structure spontaneously formed.
It is possible that a nanometer, as well as a micrometer, scale structure can be easily formed by a technique using the self-organization or self-formation phenomenon. A number of studies have therefore been made regarding this kind of technique. For example, Japanese Patent Application Laid-Open No. H10-321834 discloses a method of forming a metallic fine grain aggregate in the form of a wire by using a phenomenon in which metallic fine grains separate in a self-organization manner by their mutual electric or magnetic action.
As a method of forming fine orderly holes, anodized alumina film may be mentioned. An anodized alumina film is a porous film having fine holes grown in the film surface perpendicularly from the film surface (R. C. Furneaux, W. R. Rigby & A. P. Davidson NATURE vol. 337 P 147 (1989)). This porous oxide film is characterized by having a unique geometrical structure in which extremely fine holes having a diameter of several nanometers to several hundred nanometers are arrayed at intervals of several nanometers to several hundred nanometers generally in parallel with reach other.
These fine holes have a high aspect ratio and have improved uniformity in the diameter in their cross-sections. The diameter and the interval of these fine holes can be controlled to some degree by adjusting the current and voltage at the time of anodization.
Also, a technique of forming fine holes in an Si substrate surface by anodization of Si is generally known. Ordinarily, in this anodization, a positive voltage is applied to the substrate in a fluoric acid solution to etch and remove Si, thereby forming fine holes.
While various studies have been made on fine structures as described above, there has been a demand for a novel microstructure smaller in size and a controlled method of manufacturing such a microstructure.
For instance, the interval between fine holes in anodized alumina film is ordinarily larger than 10 nm, while the fine hole diameter is slightly smaller than 10 nm. It is extremely difficult to fabricate an orderly structure having such a size.
Also, fine holes can easily branch off in anodization of Si and only a limited number of substrates can be used. It is also difficult to obtain orderly fine, nanosized holes. Also, it is difficult to fill these fine holes with a material, such as a metal.